Grey Box Render (internal)

You clicked Render in Grey Box Studio, the panel closed, and a node you have never seen appeared in your queue with the display name Grey Box Render (internal). Nothing is broken. That node is the editor's hand reaching into ComfyUI's execution thread.

What it is

The author's own description is unusually blunt, which is a mercy: "A render from Grey Box Studio's Render menu, queued. Not for workflows: use Grey Box Shot."

That is the whole story. Grey Box Studio is a browser-side 3D editor built on a Vue frontend. It can build a set, walk characters between marks and key a camera, but it cannot touch your GPU - the panel runs in a webview, and torch work has to happen on ComfyUI's queue thread (the module docstring in the source says the quiet part out loud: "GPU work has to run on the queue's thread, not beside a sampler"). So when you hit Render, the editor serialises the job into JSON and queues this node to do the actual work.

In the source it is flagged is_dev_only=True and not_idempotent=True. Translation: the node menu hides it, and the engine won't be allowed to "cache" it. You are not meant to drag it onto a canvas.

Inputs and outputs

There is exactly one input, job, a multiline STRING holding the JSON the editor wrote. There are no outputs - it's marked as an output node so the engine actually runs it, and reports back through a UI preview instead of a socket.

Its execute does one interesting thing before it renders: it resolves the project directory and checks it. The path has to be a folder actually named greybox, sitting inside ComfyUI's user directory, where every Codex show lives. If not, it raises rather than rendering. That's a deliberate guard - the editor asks the node to write video files, so the node verifies it's writing somewhere it should be.

Installing it

You don't install this one on its own. It arrives with the pack:

cd ComfyUI/custom_nodes
git clone https://github.com/Nynxz/ComfyUI-NynxzH3

Restart ComfyUI. (The README still shows the older repo name, ComfyUI-NynxzH3Studio - the project was renamed, and the old URL redirects.) Install from ComfyUI Manager instead and it ships a pre-built frontend; clone it yourself and you need pnpm install && pnpm build inside the folder, since the editor bundle is generated from frontend/.

When it goes wrong

"Grey Box Render: not a Grey Box project folder." The job pointed somewhere that isn't a greybox directory under ComfyUI's user folder. Usually that means the project moved, or you're on a stale workflow from before a rename.

It shows up in a workflow you saved. Harmless to look at, but don't build on it. It has no sockets, so it can't feed anything, and it will re-run on every queue with whatever JSON is in the box. If you want a blocking render inside a graph - frames you can wire into H3 - use Grey Box Shot, which is the same renderer with real outputs.